1. Field of the Invention
The present invention relates to a semiconductor integrated circuit, and more particularly, to a circuit and method of generating a high voltage used in a semiconductor integrated circuit.
2. Description of the Related Art
With the development of semiconductor technology, the sizes of memory cells of semiconductor memory devices including DRAM (dynamic random access memory) have been reduced and the density of the memory cells has been increased. With this increase in density and decrease of size the external power voltage, such as a power supply voltage VCC has also decreased (for example, from 5V to 1.8V or 1.5V). Even when the power supply voltage is reduced, however, a voltage higher than the power supply voltage must be supplied to circuits, bit lines, and word lines of a semiconductor memory device. Accordingly, a high voltage generator generating a voltage higher than the power supply voltage is often required when the power supply voltage is low.
For example, when a sense amplifier is operated with a low power supply voltage, the operating speed of the sense amplifier is decreased. Thus, the sense amplifier requires a high voltage to be efficiently operated. Furthermore, a relatively higher voltage is required to increase a gate voltage for controlling the operations of transistors that execute an operation of precharging bit lines and an operation of writing data to memory cells at a high speed.
High voltage generators generally use a boost circuit to boost a voltage. However, the pumping efficiency of the boost circuit is deteriorated as the power supply voltage decreases. Accordingly, a high voltage generating circuit and method capable of maintaining pumping efficiency even with a low power supply voltage are needed.